Oscillating velocities, and energy

1. The problem statement, all variables and given/known data
A 0.40- kg mass at the end of a spring oscillates 2.9 times per second with an amplitude of 0.20m.
a)Determine the magnitude of the velocity when it passes the equilibrium point.
b)Determine the magnitude of the velocity when it is 0.10 from equilibrium.
c)Determine the total energy of the system.
d)Determine the equation describing the motion of the mass, assuming that at = 0, was a maximum and that in seconds.
1- (0.4cm)cos18t
2- (0.4cm)sin18t
3- (0.2cm)sin18t
4- (0.2cm)cos18t

3. The attempt at a solution
maybe someone can help me start heading in the right direction. im not really that sure where to start, or what equation to start with.

i calculated the k (spring constant) by manipulating the forumla T^2=4π^2m/k to k=4π^2m/T^2. using m=.4 kg, frequency=2.9→period=1/2.9=.3448. so i got k=132.81 N/m.

im thinking the energy equations are supposed to be used for parts a,b due to the way part c is worded, but i cant see how the given information relates to the oscillating energy equations.